Gas analysis apparatus



Sept; 15, 1942. Q1. HALL GAS ANALYSIS APPARATUS Filed Feb. 9, 1940 I e la H m t m fi t e A vwmwu Patented Sept. 15, 1942 2,296,030 GAS ANALYSIS APPARATUS Chester I. Hall, Schenectady, N. .Y., assignor to General Electric Company, a corporation of New York Application February 9, 1940, Serial No. 318,104

6 Claims.

This invention relates to gas analysis apparatus and more particularly to apparatus for the determination and continuous indication of the degree of or percentage purity of gases.

Heretofore, in the detection or measurement of a known constituent in a gaseous mixture by the thermal conductivity method, it has been the practice to compare the thermalconductivity of the gaseous mixture to be analyzed with that gasunder investigation but which does not neferred form, both of the temperature sensitive devices are immersed in spaced relation in the of a gas of known composition'called a stand- 10 as under investigation. I preferably mount a ard 'or reference gas. In making this com-- perforated shield or 'bafile member between the parison it is customary to employ two electrically two temperature sensitive devices to reduce radiaheated thermo-sensitive elements, such as temtion. Heat is app 0 One Of the t l perature responsive resistances, connected in two ture sensitive devices and under such conditions of the arms of a Wheatstone bridge, one of the 15 the temperature variation between the two deresistance elements being immersed in the gas vices is a function of the thermal conductivity under observation and the other being positioned of the gas. The ratio of these temperature may in a sealed envelope containing air or some other be measured by any suitable means such as a desired gas, always under fixed conditions. Unmercury manometer or temperature sensitive der such conditions the equilibrium temperaresistance elements connected in a bridge cirture attained by the thermo-sensitive elements cuit. After an empirical calibration has been will depend mainly upon. the rate of loss'of heat made the quantitative composition of the gas cf each element or the ability of the gas surmixture may be rapidly and accurately deterrounding each element to conduct heat, this temmined from this ratio. perature being lower when the gas has ahigh v The novel features which I believe to be char-,-

.thermal conductivity and higher when the gas acter'istic of the invention are set forth with has a low conductivity. If the temperature sensiparticularity in the appended claims. My inventive element has a high temperature coefficient-of tion itself, however, both as to its organization electrical resistance, this resistance will have a and method of operation together with further value dependent onthe thermal conductivity and objects and advantages thereof may be best unwillthereforecorrespond to the composition of the derstood by reference to the following descripsurrounding gas. Thus, if the two-temperature tion when considered in connection with the acsensitive resistance elements are exposed to gases companying drawing.

.having different thermal conductivities, the In the drawing, Figs. 1 to '3 illustrate appaquantities of heatgiven off by or the rate of heat ratus arranged to operate in accordance with loss of each of these elements to the respective the principles of my invention. Figs. 4 to 6 ilgases will be different, with the result that one lustrate a modified form of apparatus whereby of the resistance elements will be maintained at the temperatures of the temperature responsive a higher temperature than the other. This difelements may be compared electrically. ference in temperature will result in a difference 40 The apparatus shown in Figs. 1 and 2 comin the resistance of thetwo elements thereby prises a container or chamber II havingan incausing a deflection of a galvanometer in the let I2 and an outlet I3 through which passes the bridgecircuit or necessitating an adjustment of gas to be investigated. The chamber is further the bridge to produce a state of balance, the conveniently formed into two sections l5 and I6 magnitude of this deflection or adjustment being '45 by means of a shield or bailie member I! havdependent upon the difference between the-thering perforations ll' therein and composed of a mal conductivities of the two gases. suitable 'material such as polished aluminum.

It is an object of my invention to provide a By using a material of this'character radiation new and improved apparatus for determining and -may be reduced to a minimum. It is well known continuously indicating the degree of or perto those skilled in the'art that a surface-such centage purity of a given gas. as that of a polished aluminum plate is a high- It is another object of my, inventionto pro ly eflicient reflector of radiant energy and has vide improved apparatus for analyzing gases a proportionately low capacity for absorption which depends on the thermal conductivity of the of radiant energy. Such a V baiile, therefore,

greatly diminishes radiation from one section to the other of the chamber II and likewise diminishes radiation from an object in one section to an object in the other. Each of the sections l5 and I6 communicates with the inlet and outlet I2 and I3, respectively.

I provide a difierential temperature measuring device for comparing the temperatures of the surrounding gas in each of the sections l5 and lint the chamber II. In the illustrated embodiment this comprises a manometer M including a tube |8- of U-shape terminating at its ends in bulbs l9 and 20, which bulbs are mounted in sealed relation in the sections l5 and I6, respectively. In the bottom portion of the tube l8 mercury or other liquid 2| is placed and the resulting mercury column serves as an indicator of the temperature difference. The bulbs or sealed'containers l9 and 20 are filled with a gas such as hydrogen, nitrogen or argon which will respond by pressure differences to the difierence in temperature between or the ratio of the temperatures of the two bulbs. This will cause a ,shift of the mercury column'until the pressures are again balanced.

About one of the bulb or sealed containers, such as 20, there is positioned a heating element 22 in the form of a coil to which heat is supplied at a uniform rate. The maintenance of constancy of heat input to the coil 22 being important as a calibration characteristic of the device, the coil is therefore adapted to be energized from a suitable source of regulated voltage which in the illustration shown comprisesa voltage regulating transformer T energized by a source of alternating current 23 and consisting essentiallyof a capacitor C and a winding P in series, the winding P having a saturable core sistance material having a zero temperature coefficient or electrical resistivity.

The differential temperature measuring device M is provided with a scale 25 for indicating the height 01' the mercury column 2| in terms of the percentage or degree of purity of the gas being investigated. The temperature measuringdevice is further provided with a series of contact elements 26, 21 and 28 which make contact with the mercury column 2| under certain conditions of operation presently to be described. I

In operation, assume that the gas to be investigated is being passed through the chamber II and that it flows therethrough in the two similar sections l5 and I6. Assume further that the heating element 22 is energized to supply heat to the bulb 20. Since both of the bulbs or sealed containers l9 and 20 are continuously surrounded by the gas to be tested, the temperature ditl'erence between the bulbs is determined by the thermal conductivity of the gas enclosed between them and the outer enclosing envelope H where radiation takes place. conductivity of .the gas being tested, the greater will be the temperature difference between the two bulbs l9 and 20.

The regulated or sub-" determine the percentage purity of a gas such as hydrogen in a mixture with air. On account of the fact that the thermal conductivity of hydrogen is approximately 6 or '1 times that of dry air, the presence of pure hydrogen in the enclosing envelope I will cause a minimum temperature difierence between the two bulbs due to rapid radiation from the bulb 20 and conduction through the gas of the heat delivered to the bulb 20 by the heating element 22. If now the hydrogen is removed andair substituted, because of the lower thermal conductivity or improved insulating qualities of air as compared to that of hydrogen, the heat delivered to the heated bulb 20 will be dissipated at a proportionally lower rate with the result that the temperature difierence between the two bulbs will greatly increase. Intermediate values of dilution of the hydrogen with air will produce corresponding intermediate thermal conductivities, thus making it possible to calibrate the device in percentage or degree of purity of hydrogen with relation to the temperature difference between the two bulbs l9 and 20.

As already explained, upon a difference in temperature between the two bulbs I9 and 20, the pressure of the gases enclosed by the bulbs undergoes a relative change, thereby causing a shift of the mercury column 2| until the pressures ar again in balance; The height of the mercury column thus becomes an indication of the purity of the hydrogen or other gas surrounding the two bulbs. By providing sealed-in contacts, such as 26 and 21 at definite points, for instance, at a point corresponding to 85 per cent purity of the gas being investigated, a visual or audible signal may be operated to warn of the approach of a dangerous condition. Fig. 3 illustrates the manometer M for this condition with the mercury column 2| shifted to close the contact 21 thereby energizing an indicator or signal device 29 through a circuit including a source of supply 30, the lower contact 26, and the mercury column 2|.

When the mercury column 2| stands at the same height in each of the legs of the U corresponding to the condition where the pressures of the two bulbs l9 and 20 are equal, as depicted in Fig. 1, a second contact 28 is closed to energize an.indicating or signaling device 3| from the source of supply 30 through a circuit including the lower contact 26 and the'mercury column 2|. The condition where the pressures of pressures. This arrangement thus serves as an indication of the failure of the mechanism.

InFigs. 4 and 5 I have illustrated a modification in which a plurality of temperature respon- The lower thethermal a an illustration. assume that it is desired to'75 sive resistance elements are immersed in the surrounding gas in the sections I5 and l6 or the chamber II. A- type or temperature responsive devicewhicl may be used with highly satisfactory results is one of the character described and claimed in a copending application of Chester I. Hall, Serial No. 281,856 filed June 29,1939, entitled Temperature responsive device. A device scribed.

elements.

vices such as 36, there is provided a heating element 22 energized from the source 23 through a variable impedance device 24, as already de- As indicated in the sectional elevation view of Fig. 5, each of the temperature responsive devices 35 and 36 comprises a pair of electrodes 31 material to give different desirable physical characteristics, an example of which is illustrated by the materials disclosed in the co-pending application already referred to. However, various other resistance materials are well known in the art and it is not my intention to limit the invention to the employment of any particular composition of resistance material in the thermoqsensitive As illustrated in Fig. 5, the temperature responsive elements 35 and 36 are mounted in the wall portion 40 of the chamber II and electrically insulated therefrom by a suitable means such as a sleeve 4L A pair of terminals 42 and 43 connected respectively to the electrodes 31 and 38 aresuitably mounted in an insulated mem- '36 are heated from the source of supply 45, heat is also applied to the element 36 by the auxiliary heating element 24, and a calibration of the instrument 49 is madeusing gases of known constituents. For the normal operatingconditiom intermediate position with reference to the contacts 27' and 28'. ,Then when the percentage purity of. the constituent being tested drops to a predetermined minimum value, such, or instance, as the 85 per cent value in the .case of hydrogen in air, the contacts 26 and 21 will close to operate the visual" or audible signal 29 to warn of the approach of a dangerous condition. Similarly, the contact 28 may be adjusted to make contact with the movable contact 26' for the condition when either the energization of the bridge or the heater circuit to the element 38 has been discontinued, thereby energizing the visual or audible signal 3I toindicate failure of the mechanism. When the heater circuit is discontinued the two ther rno-sensitive elements will then be atF-the same' temperature. -.The bridge may, therefore, be so adjusted that the, contacts 26' and 28' close for this condition.

Because of the fact that the rate of heat dissipation from the heated bulb or the element 36 will also depend to a certain extent upon the ber 44.' Devices employing resistance materials.

of the character disclosed in my copending application are characterized by comparatively large variations in resistance with temperature changes and for this reason they are highly satisiactory for use in carrying out the principle of my invention. e

I provide suitable means for determining theratio of the resistances of the elements and 36 with variations in temperature. As illustrated in Fig. 6, the temperature sensitive elements 35 and 36 are connected in series circuit relation with each other and in parallel relation with the secondary winding 45 of. a. transformer 46 in a Wheatstone bridge circuit. The transformer 46 is energized through its primary winding 41 by a substantially constant alternating current source of supply 48. Connected between the two temperature sensitive elements 35 and 36 and the rate of flow of the gas through the chamber II, it will be appreciated that the rate of flow should be maintained substantially constant. Any suitable device may be employed for this purpose, many of which are well known to those skilled in the art.

It may be pointed out thatthe gas entrance and exits to the chamber l I may be positioned at 90 degrees to their present positions so that the gas enters and leaves on each side 01' the baiile member. In this event, however, the balile need not be perforated provided the gas is uniformly delivered to both sections of the chamber.

In accordance with the present invention wherein both of the temperature responsive elements are immersed in the same gas corresponding to the gas to be tested and the device is initially calibrated with reference to known purimid-section of the secondary winding and in-,

fiuenced by the unbalanced condition of the bridge is a suitable current responsive device 49 6 having a pointer 50 cooperating with an indicating scale 5|. 'A variable connection 52 may be provided for adjusting the instrument 5| to give the desired scale reading for known conditions.

The current responsive device 49 is illustrated as being of. the contact-making type having a down-scale contact 28 and an up-scale contact 21' which cooperate with a movable contact 26 carried by the pointer.50. A suitable contactmaking instrument which may be employed is one of the character described in the United'States Letters Patent to Richard Dietze, No. 1,913,194. The contacts 21' and 28' may be made adjustable to close at predetermined values of current which, taking the foregoing illustration as an'exarnple, would be at a value of current corresponding respectively to per cent purity and that value of curren't corresponding to the condition when the resistance ort'emperature of both elements 3 and 36 are equal.

In operation, the resistance elements. 35 and I wish to point out that my invention has nu-I merous other useful applications. It may be stated generally that the invention may be used with highly satisfactory results in those instances where the components of the gas 'difier material.- ly in thermal conductivity. For example, it may be used in the determination of hydrogen in electrolytic oxygen, hydrogen in electrolytic chlorine, and oxygen in electrolytic hydrogen. Other I illustrations of useful applications are the determination of the percentage of hydrogen in water gas and in the mixture of nitrogen, hy-

drogen, and carbon monoxide existing in one of the synthetic ammonia processes. The conduc-.

tivities of nitrogen and carbon monoxide lie very 1 close together, while that of hydrogen is relatively very great. Consequently, the relative prop0rtions of nitrogen and carbon monoxide make little difference in the determination of. the amount of hydrogen present. The same relation is practically true in the case of the determination of carbon dioxide in boiler flue gases so that this also forms a useful field of application. These gases are composed principally of water vapor,

carbon dioxide, oxygen, nitrogen and sometimes small amounts of carbon monoxide. The thermal conductivities of nitrogen, oxygen, and carbon monoxide are of nearly the same values while that of carbon dioxide is considerably lower. The device may also be successfully applied to the determination of the amount of air in balloon gas, and also to the testing of the porosity or permeability of balloon or other fabrics by adapting the device in accordance with the teachings of the Shakespear Patent 1,304,208.

While I have illustrated and particularly described certain embodiments of my invention and certain methods embraced therein for the purpose of explaining its principle and showing its application, it will be obvious to those skilled in the art that many modifications and variations are possible and I intend in the appended claims to cover all such modifications and variations which do not depart from the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In gas analysis apparatus, a chamber adapted to contain a gas having a known constituent the percentage purity of which is to be investigated, a plurality of devices positioned in said chamber in spaced relation and exposed to said gas, said devices each having a characteristic which is variable in accordance with changes in temperature, means for applying heat to one ments, and means for obtaining a measurement oithe temperature variations in said elements.

3. In apparatus for the detection and measurement of gases, a chamber containing the gas to be tested, a pair of thermo-sensitive elements positioned in said chamber in spaced relation and exposed to said gas, a radiation diminishing baffle member mounted between said thermo-sensitive elements, means for applying heatto one.

oi said thermo-sensitive elements, and means responsive to the temperature difference between said thermo-sensitive elements.

4. In gas analysis apparatus, a chamber adapted to contain a gas the percentage purity of one constituent of which is to be tested, a plurality of devices positioned in said chamber in spaced relation and exposed to said gas, said devices having characteristics which vary in accordance with changes in temperature, a heater in thermal relation to one of said devices, and means responsive to a predetermined diiierence in the characteristics of said devices.

5. In a device for determining the percentage purity of a known constitu nt in a gaseous mixture', a chamber containing said gaseous mixture,

a plurality of thermo-sensitive elements positioned in spaced relation in said chamber and exposed to said gas, means for applying heat to one of said elements, and means in thermal relation to these elements responsive to equalization of the temperatures thereof for indicating a discontinuance of operation of said heat applying means and a state of inoperativeness of the device.

6. In gas analysis apparatus, a chamber adapted to contain a gas having a known constituent, the percentage purity of which is to be investigated, a plurality 01' devices positioned in said chamber in spaced relation and exposed to said gas, the said devices each having a characteristic which is variable in accordance with changes in temperatures, a radiation diminishing shield between said devices, a heater in thermal relation to only one of said devices, and a characteristic-rneasuring device in operative relation to both of said devicesfor producing an eflect responsive to variation in relative characteristics or said devices when the gas to which they are exposed is changed.

CHESTER I. HALL. 

